[PATCH v2] Add gdb::nullopt, from C++17's std::nullopt
Christian Biesinger
cbiesinger@google.com
Tue Jun 2 20:27:36 GMT 2020
Ping? Simon/Pedro, any thoughts?
On Tue, May 19, 2020 at 2:27 PM <cbiesinger@chromium.org> wrote:
>
> From: Christian Biesinger <cbiesinger@google.com>
>
> [Fixes formatting and a compile error, I guess I never compiled the
> final version I sent :( Also enables the nullopt unit tests.]
>
> This provides a clearer way to initialize a gdb::optional. E.g.:
>
> gdb::optional<foo> bar () {
> return gdb::nullopt;
> }
>
> or
>
> void foo (gdb::optional<bar>) {
> }
>
> foo (gdb::nullopt);
>
> Also updates all places I could find that use {} or optional() to instead
> use nullopt.
>
> gdb/ChangeLog:
>
> 2020-05-19 Christian Biesinger <cbiesinger@google.com>
>
> * cli/cli-option.c (struct option_def_and_value): Update to use nullopt.
> (parse_option): Likewise.
> * dwarf2/die.h (struct die_info): Likewise.
> * dwarf2/read.c (dw2_expand_symtabs_for_function): Likewise.
> (dw2_debug_names_expand_symtabs_for_function): Likewise.
> (lookup_dwo_id): Likewise.
> * fbsd-tdep.c (fbsd_make_note_desc): Likewise.
> * inf-child.c (inf_child_target::fileio_readlink): Likewise.
> * linux-nat.c (linux_nat_target::fileio_readlink): Likewise.
> * python/python.c (gdbpy_colorize): Likewise.
> * remote.c (remote_target::fileio_readlink): Likewise.
> * solib-aix.c (solib_aix_parse_libraries): Likewise.
> * solib-svr4.c (read_program_header): Likewise.
> (read_program_headers_from_bfd): Likewise.
> * symtab.h (struct general_symbol_info): Likewise.
> * target.c (target_read_alloc_1): Likewise.
> (target_read_stralloc): Likewise.
> (target_get_osdata): Likewise.
> (target_ops::fileio_readlink): Likewise.
> (target_fileio_readlink): Likewise.
> * unittests/optional/assignment/5.cc: Enable nullopt unittests.
> * xml-support.c (xml_fetch_content_from_file): Likewise.
> * xml-tdesc.c (target_fetch_description_xml): Likewise.
> (string_read_description_xml): Likewise.
>
> gdbsupport/ChangeLog:
>
> 2020-05-19 Christian Biesinger <cbiesinger@google.com>
>
> * gdb_optional.h (struct nullopt_t): Add.
> (nullopt): Add.
> (class optional): Add nullopt_t constructor.
>
> Change-Id: I371f05484a3b85cc6d54a8baead2b4f64e6ee308
> ---
> gdb/cli/cli-option.c | 24 ++++++++++++------------
> gdb/dwarf2/die.h | 2 +-
> gdb/dwarf2/read.c | 7 ++++---
> gdb/fbsd-tdep.c | 2 +-
> gdb/inf-child.c | 4 ++--
> gdb/linux-nat.c | 2 +-
> gdb/python/python.c | 20 ++++++++++----------
> gdb/remote.c | 4 ++--
> gdb/solib-aix.c | 4 ++--
> gdb/solib-svr4.c | 24 ++++++++++++------------
> gdb/symtab.h | 3 +--
> gdb/target.c | 10 +++++-----
> gdb/unittests/optional/assignment/5.cc | 10 +++-------
> gdb/xml-support.c | 4 ++--
> gdb/xml-tdesc.c | 7 ++++---
> gdbsupport/gdb_optional.h | 16 ++++++++++++++++
> 16 files changed, 78 insertions(+), 65 deletions(-)
>
> diff --git a/gdb/cli/cli-option.c b/gdb/cli/cli-option.c
> index a24eca457d..08457e4e03 100644
> --- a/gdb/cli/cli-option.c
> +++ b/gdb/cli/cli-option.c
> @@ -62,7 +62,7 @@ struct option_def_and_value
>
> /* Constructor. */
> option_def_and_value (const option_def &option_, void *ctx_,
> - gdb::optional<option_value> &&value_ = {})
> + gdb::optional<option_value> &&value_ = gdb::nullopt)
> : option (option_),
> ctx (ctx_),
> value (std::move (value_))
> @@ -185,15 +185,15 @@ parse_option (gdb::array_view<const option_def_group> options_group,
> parse_option_completion_info *completion = nullptr)
> {
> if (*args == nullptr)
> - return {};
> + return gdb::nullopt;
> else if (**args != '-')
> {
> if (have_delimiter)
> error (_("Unrecognized option at: %s"), *args);
> - return {};
> + return gdb::nullopt;
> }
> else if (check_for_argument (args, "--"))
> - return {};
> + return gdb::nullopt;
>
> /* Skip the initial '-'. */
> const char *arg = *args + 1;
> @@ -216,7 +216,7 @@ parse_option (gdb::array_view<const option_def_group> options_group,
> complete_on_options (options_group,
> completion->tracker,
> arg, completion->word);
> - return {};
> + return gdb::nullopt;
> }
>
> error (_("Ambiguous option at: -%s"), arg);
> @@ -237,14 +237,14 @@ parse_option (gdb::array_view<const option_def_group> options_group,
> if (have_delimiter || mode != PROCESS_OPTIONS_UNKNOWN_IS_OPERAND)
> error (_("Unrecognized option at: %s"), *args);
>
> - return {};
> + return gdb::nullopt;
> }
>
> if (completion != nullptr && arg[len] == '\0')
> {
> complete_on_options (options_group, completion->tracker,
> arg, completion->word);
> - return {};
> + return gdb::nullopt;
> }
>
> *args += 1 + len;
> @@ -347,7 +347,7 @@ parse_option (gdb::array_view<const option_def_group> options_group,
> };
> complete_on_enum (completion->tracker, all_boolean_enums,
> val_str, val_str);
> - return {};
> + return gdb::nullopt;
> }
> }
>
> @@ -370,13 +370,13 @@ parse_option (gdb::array_view<const option_def_group> options_group,
> (make_unique_xstrdup ("NUMBER"));
> completion->tracker.add_completion
> (make_unique_xstrdup ("unlimited"));
> - return {};
> + return gdb::nullopt;
> }
> else if (startswith ("unlimited", *args))
> {
> completion->tracker.add_completion
> (make_unique_xstrdup ("unlimited"));
> - return {};
> + return gdb::nullopt;
> }
> }
>
> @@ -403,7 +403,7 @@ parse_option (gdb::array_view<const option_def_group> options_group,
> complete_on_enum (completion->tracker,
> match->enums, *args, *args);
> if (completion->tracker.have_completions ())
> - return {};
> + return gdb::nullopt;
>
> /* If we don't have completions, let the
> non-completion path throw on invalid enum value
> @@ -448,7 +448,7 @@ parse_option (gdb::array_view<const option_def_group> options_group,
> gdb_assert_not_reached (_("option type not supported"));
> }
>
> - return {};
> + return gdb::nullopt;
> }
>
> /* See cli-option.h. */
> diff --git a/gdb/dwarf2/die.h b/gdb/dwarf2/die.h
> index 5522ebdf31..9f3a877e73 100644
> --- a/gdb/dwarf2/die.h
> +++ b/gdb/dwarf2/die.h
> @@ -45,7 +45,7 @@ struct die_info
> /* If both exist, just use the first one. */
> return DW_UNSND (&attrs[i]);
> }
> - return gdb::optional<ULONGEST> ();
> + return gdb::nullopt;
> }
>
> /* Return range lists base of the compile unit, which, if exists, is
> diff --git a/gdb/dwarf2/read.c b/gdb/dwarf2/read.c
> index 719051bc5b..13c485b15d 100644
> --- a/gdb/dwarf2/read.c
> +++ b/gdb/dwarf2/read.c
> @@ -3586,7 +3586,8 @@ dw2_expand_symtabs_for_function (struct objfile *objfile,
> struct dw2_symtab_iterator iter;
> struct dwarf2_per_cu_data *per_cu;
>
> - dw2_symtab_iter_init (&iter, dwarf2_per_objfile, {}, VAR_DOMAIN, func_name);
> + dw2_symtab_iter_init (&iter, dwarf2_per_objfile, gdb::nullopt, VAR_DOMAIN,
> + func_name);
>
> while ((per_cu = dw2_symtab_iter_next (&iter)) != NULL)
> dw2_instantiate_symtab (per_cu, false);
> @@ -5624,7 +5625,7 @@ dw2_debug_names_expand_symtabs_for_function (struct objfile *objfile,
> {
> const mapped_debug_names &map = *dwarf2_per_objfile->debug_names_table;
>
> - dw2_debug_names_iterator iter (map, {}, VAR_DOMAIN, func_name);
> + dw2_debug_names_iterator iter (map, gdb::nullopt, VAR_DOMAIN, func_name);
>
> struct dwarf2_per_cu_data *per_cu;
> while ((per_cu = iter.next ()) != NULL)
> @@ -6760,7 +6761,7 @@ lookup_dwo_id (struct dwarf2_cu *cu, struct die_info* comp_unit_die)
> struct attribute *attr;
> attr = dwarf2_attr (comp_unit_die, DW_AT_GNU_dwo_id, cu);
> if (attr == nullptr)
> - return gdb::optional<ULONGEST> ();
> + return gdb::nullopt;
> return DW_UNSND (attr);
> }
>
> diff --git a/gdb/fbsd-tdep.c b/gdb/fbsd-tdep.c
> index acf787c706..b8275814af 100644
> --- a/gdb/fbsd-tdep.c
> +++ b/gdb/fbsd-tdep.c
> @@ -694,7 +694,7 @@ fbsd_make_note_desc (enum target_object object, uint32_t structsize)
> gdb::optional<gdb::byte_vector> buf =
> target_read_alloc (current_top_target (), object, NULL);
> if (!buf || buf->empty ())
> - return {};
> + return gdb::nullopt;
>
> if (structsize == 0)
> return buf;
> diff --git a/gdb/inf-child.c b/gdb/inf-child.c
> index 4833094889..3420398f82 100644
> --- a/gdb/inf-child.c
> +++ b/gdb/inf-child.c
> @@ -381,13 +381,13 @@ inf_child_target::fileio_readlink (struct inferior *inf, const char *filename,
> if (len < 0)
> {
> *target_errno = host_to_fileio_error (errno);
> - return {};
> + return gdb::nullopt;
> }
>
> return std::string (buf, len);
> #else
> *target_errno = FILEIO_ENOSYS;
> - return {};
> + return gdb::nullopt;
> #endif
> }
>
> diff --git a/gdb/linux-nat.c b/gdb/linux-nat.c
> index 0a2bfdc57d..8de9501639 100644
> --- a/gdb/linux-nat.c
> +++ b/gdb/linux-nat.c
> @@ -4480,7 +4480,7 @@ linux_nat_target::fileio_readlink (struct inferior *inf, const char *filename,
> if (len < 0)
> {
> *target_errno = host_to_fileio_error (errno);
> - return {};
> + return gdb::nullopt;
> }
>
> return std::string (buf, len);
> diff --git a/gdb/python/python.c b/gdb/python/python.c
> index 67f362b852..c241a09f71 100644
> --- a/gdb/python/python.c
> +++ b/gdb/python/python.c
> @@ -1120,35 +1120,35 @@ static gdb::optional<std::string>
> gdbpy_colorize (const std::string &filename, const std::string &contents)
> {
> if (!gdb_python_initialized)
> - return {};
> + return gdb::nullopt;
>
> gdbpy_enter enter_py (get_current_arch (), current_language);
>
> if (gdb_python_module == nullptr
> || !PyObject_HasAttrString (gdb_python_module, "colorize"))
> - return {};
> + return gdb::nullopt;
>
> gdbpy_ref<> hook (PyObject_GetAttrString (gdb_python_module, "colorize"));
> if (hook == nullptr)
> {
> gdbpy_print_stack ();
> - return {};
> + return gdb::nullopt;
> }
>
> if (!PyCallable_Check (hook.get ()))
> - return {};
> + return gdb::nullopt;
>
> gdbpy_ref<> fname_arg (PyString_FromString (filename.c_str ()));
> if (fname_arg == nullptr)
> {
> gdbpy_print_stack ();
> - return {};
> + return gdb::nullopt;
> }
> gdbpy_ref<> contents_arg (PyString_FromString (contents.c_str ()));
> if (contents_arg == nullptr)
> {
> gdbpy_print_stack ();
> - return {};
> + return gdb::nullopt;
> }
>
> gdbpy_ref<> result (PyObject_CallFunctionObjArgs (hook.get (),
> @@ -1158,17 +1158,17 @@ gdbpy_colorize (const std::string &filename, const std::string &contents)
> if (result == nullptr)
> {
> gdbpy_print_stack ();
> - return {};
> + return gdb::nullopt;
> }
>
> if (!gdbpy_is_string (result.get ()))
> - return {};
> + return gdb::nullopt;
>
> gdbpy_ref<> unic = python_string_to_unicode (result.get ());
> if (unic == nullptr)
> {
> gdbpy_print_stack ();
> - return {};
> + return gdb::nullopt;
> }
> gdbpy_ref<> host_str (PyUnicode_AsEncodedString (unic.get (),
> host_charset (),
> @@ -1176,7 +1176,7 @@ gdbpy_colorize (const std::string &filename, const std::string &contents)
> if (host_str == nullptr)
> {
> gdbpy_print_stack ();
> - return {};
> + return gdb::nullopt;
> }
>
> return std::string (PyBytes_AsString (host_str.get ()));
> diff --git a/gdb/remote.c b/gdb/remote.c
> index 312a03c8fb..b910f7e533 100644
> --- a/gdb/remote.c
> +++ b/gdb/remote.c
> @@ -12257,7 +12257,7 @@ remote_target::fileio_readlink (struct inferior *inf, const char *filename,
> int read_len;
>
> if (remote_hostio_set_filesystem (inf, remote_errno) != 0)
> - return {};
> + return gdb::nullopt;
>
> remote_buffer_add_string (&p, &left, "vFile:readlink:");
>
> @@ -12269,7 +12269,7 @@ remote_target::fileio_readlink (struct inferior *inf, const char *filename,
> &attachment_len);
>
> if (len < 0)
> - return {};
> + return gdb::nullopt;
>
> std::string ret (len, '\0');
>
> diff --git a/gdb/solib-aix.c b/gdb/solib-aix.c
> index 125c8960c2..16cf235a20 100644
> --- a/gdb/solib-aix.c
> +++ b/gdb/solib-aix.c
> @@ -108,7 +108,7 @@ solib_aix_parse_libraries (const char *library)
> "at compile time"));
> }
>
> - return {};
> + return gdb::nullopt;
> }
>
> #else /* HAVE_LIBEXPAT */
> @@ -215,7 +215,7 @@ solib_aix_parse_libraries (const char *library)
> library_list_elements, library, &result) == 0)
> return result;
>
> - return {};
> + return gdb::nullopt;
> }
>
> #endif /* HAVE_LIBEXPAT */
> diff --git a/gdb/solib-svr4.c b/gdb/solib-svr4.c
> index 19d1105ae9..6df604cc2f 100644
> --- a/gdb/solib-svr4.c
> +++ b/gdb/solib-svr4.c
> @@ -429,13 +429,13 @@ read_program_header (int type, int *p_arch_size, CORE_ADDR *base_addr)
>
> /* Get required auxv elements from target. */
> if (target_auxv_search (current_top_target (), AT_PHDR, &at_phdr) <= 0)
> - return {};
> + return gdb::nullopt;
> if (target_auxv_search (current_top_target (), AT_PHENT, &at_phent) <= 0)
> - return {};
> + return gdb::nullopt;
> if (target_auxv_search (current_top_target (), AT_PHNUM, &at_phnum) <= 0)
> - return {};
> + return gdb::nullopt;
> if (!at_phdr || !at_phnum)
> - return {};
> + return gdb::nullopt;
>
> /* Determine ELF architecture type. */
> if (at_phent == sizeof (Elf32_External_Phdr))
> @@ -443,7 +443,7 @@ read_program_header (int type, int *p_arch_size, CORE_ADDR *base_addr)
> else if (at_phent == sizeof (Elf64_External_Phdr))
> arch_size = 64;
> else
> - return {};
> + return gdb::nullopt;
>
> /* Find the requested segment. */
> if (type == -1)
> @@ -463,7 +463,7 @@ read_program_header (int type, int *p_arch_size, CORE_ADDR *base_addr)
>
> if (target_read_memory (at_phdr + i * sizeof (phdr),
> (gdb_byte *)&phdr, sizeof (phdr)))
> - return {};
> + return gdb::nullopt;
>
> p_type = extract_unsigned_integer ((gdb_byte *) phdr.p_type,
> 4, byte_order);
> @@ -480,7 +480,7 @@ read_program_header (int type, int *p_arch_size, CORE_ADDR *base_addr)
> }
>
> if (i == at_phnum)
> - return {};
> + return gdb::nullopt;
>
> /* Retrieve address and size. */
> sect_addr = extract_unsigned_integer ((gdb_byte *)phdr.p_vaddr,
> @@ -500,7 +500,7 @@ read_program_header (int type, int *p_arch_size, CORE_ADDR *base_addr)
>
> if (target_read_memory (at_phdr + i * sizeof (phdr),
> (gdb_byte *)&phdr, sizeof (phdr)))
> - return {};
> + return gdb::nullopt;
>
> p_type = extract_unsigned_integer ((gdb_byte *) phdr.p_type,
> 4, byte_order);
> @@ -517,7 +517,7 @@ read_program_header (int type, int *p_arch_size, CORE_ADDR *base_addr)
> }
>
> if (i == at_phnum)
> - return {};
> + return gdb::nullopt;
>
> /* Retrieve address and size. */
> sect_addr = extract_unsigned_integer ((gdb_byte *)phdr.p_vaddr,
> @@ -539,7 +539,7 @@ read_program_header (int type, int *p_arch_size, CORE_ADDR *base_addr)
> /* Read in requested program header. */
> gdb::byte_vector buf (sect_size);
> if (target_read_memory (sect_addr, buf.data (), sect_size))
> - return {};
> + return gdb::nullopt;
>
> if (p_arch_size)
> *p_arch_size = arch_size;
> @@ -2510,12 +2510,12 @@ read_program_headers_from_bfd (bfd *abfd)
> Elf_Internal_Ehdr *ehdr = elf_elfheader (abfd);
> int phdrs_size = ehdr->e_phnum * ehdr->e_phentsize;
> if (phdrs_size == 0)
> - return {};
> + return gdb::nullopt;
>
> gdb::byte_vector buf (phdrs_size);
> if (bfd_seek (abfd, ehdr->e_phoff, SEEK_SET) != 0
> || bfd_bread (buf.data (), phdrs_size, abfd) != phdrs_size)
> - return {};
> + return gdb::nullopt;
>
> return buf;
> }
> diff --git a/gdb/symtab.h b/gdb/symtab.h
> index 05e6a311b8..3a1200cfa1 100644
> --- a/gdb/symtab.h
> +++ b/gdb/symtab.h
> @@ -471,8 +471,7 @@ struct general_symbol_info
> copy_name must be set to true. */
> void compute_and_set_names (gdb::string_view linkage_name, bool copy_name,
> struct objfile_per_bfd_storage *per_bfd,
> - gdb::optional<hashval_t> hash
> - = gdb::optional<hashval_t> ());
> + gdb::optional<hashval_t> hash = gdb::nullopt);
>
> /* Name of the symbol. This is a required field. Storage for the
> name is allocated on the objfile_obstack for the associated
> diff --git a/gdb/target.c b/gdb/target.c
> index 6982a806e3..67e26fb46d 100644
> --- a/gdb/target.c
> +++ b/gdb/target.c
> @@ -1781,7 +1781,7 @@ target_read_alloc_1 (struct target_ops *ops, enum target_object object,
> else if (status != TARGET_XFER_OK)
> {
> /* An error occurred. */
> - return {};
> + return gdb::nullopt;
> }
>
> buf_pos += xfered_len;
> @@ -1809,7 +1809,7 @@ target_read_stralloc (struct target_ops *ops, enum target_object object,
> = target_read_alloc_1<char> (ops, object, annex);
>
> if (!buf)
> - return {};
> + return gdb::nullopt;
>
> if (buf->empty () || buf->back () != '\0')
> buf->push_back ('\0');
> @@ -2536,7 +2536,7 @@ target_get_osdata (const char *type)
> t = find_default_run_target ("get OS data");
>
> if (!t)
> - return {};
> + return gdb::nullopt;
>
> return target_read_stralloc (t, TARGET_OBJECT_OSDATA, type);
> }
> @@ -2772,7 +2772,7 @@ target_ops::fileio_readlink (struct inferior *inf, const char *filename,
> int *target_errno)
> {
> *target_errno = FILEIO_ENOSYS;
> - return {};
> + return gdb::nullopt;
> }
>
> /* Helper for target_fileio_open and
> @@ -2984,7 +2984,7 @@ target_fileio_readlink (struct inferior *inf, const char *filename,
> }
>
> *target_errno = FILEIO_ENOSYS;
> - return {};
> + return gdb::nullopt;
> }
>
> /* Like scoped_fd, but specific to target fileio. */
> diff --git a/gdb/unittests/optional/assignment/5.cc b/gdb/unittests/optional/assignment/5.cc
> index 74d06ae568..4b39b63b54 100644
> --- a/gdb/unittests/optional/assignment/5.cc
> +++ b/gdb/unittests/optional/assignment/5.cc
> @@ -33,23 +33,19 @@ test ()
> {
> using O = gdb::optional<value_type>;
>
> - // Check std::nullopt_t and 'default' (= {}) assignment
> + // Check gdb::nullopt_t and 'default' (= {}) assignment
>
> -#ifndef GDB_OPTIONAL
> {
> O o;
> - o = std::nullopt;
> + o = gdb::nullopt;
> VERIFY( !o );
> }
> -#endif
>
> -#ifndef GDB_OPTIONAL
> {
> O o { gdb::in_place };
> - o = std::nullopt;
> + o = gdb::nullopt;
> VERIFY( !o );
> }
> -#endif
>
> #ifndef GDB_OPTIONAL
> {
> diff --git a/gdb/xml-support.c b/gdb/xml-support.c
> index c906b69fda..5177315be5 100644
> --- a/gdb/xml-support.c
> +++ b/gdb/xml-support.c
> @@ -984,7 +984,7 @@ xml_fetch_content_from_file (const char *filename, void *baton)
> file = gdb_fopen_cloexec (filename, FOPEN_RB);
>
> if (file == NULL)
> - return {};
> + return gdb::nullopt;
>
> /* Read in the whole file. */
>
> @@ -1001,7 +1001,7 @@ xml_fetch_content_from_file (const char *filename, void *baton)
> || ferror (file.get ()))
> {
> warning (_("Read error from \"%s\""), filename);
> - return {};
> + return gdb::nullopt;
> }
>
> text.back () = '\0';
> diff --git a/gdb/xml-tdesc.c b/gdb/xml-tdesc.c
> index 6f108a4e3e..2d47f52b16 100644
> --- a/gdb/xml-tdesc.c
> +++ b/gdb/xml-tdesc.c
> @@ -730,12 +730,12 @@ target_fetch_description_xml (struct target_ops *ops)
> "disabled at compile time"));
> }
>
> - return {};
> + return gdb::nullopt;
> #else
> gdb::optional<gdb::char_vector>
> tdesc_str = fetch_available_features_from_target ("target.xml", ops);
> if (!tdesc_str)
> - return {};
> + return gdb::nullopt;
>
> std::string output;
> if (!xml_process_xincludes (output,
> @@ -744,7 +744,7 @@ target_fetch_description_xml (struct target_ops *ops)
> fetch_available_features_from_target, ops, 0))
> {
> warning (_("Could not load XML target description; ignoring"));
> - return {};
> + return gdb::nullopt;
> }
> return output;
> #endif
> @@ -758,6 +758,7 @@ string_read_description_xml (const char *xml)
> return tdesc_parse_xml (xml, [] (const char *href, void *baton)
> {
> error (_("xincludes are unsupported with this method"));
> + // We can't use nullopt here because that messes with the type inference.
> return gdb::optional<gdb::char_vector> ();
> }, nullptr);
> }
> diff --git a/gdbsupport/gdb_optional.h b/gdbsupport/gdb_optional.h
> index 02a87f6ee4..3d8030c754 100644
> --- a/gdbsupport/gdb_optional.h
> +++ b/gdbsupport/gdb_optional.h
> @@ -25,12 +25,18 @@
> namespace gdb
> {
>
> +struct nullopt_t
> +{
> + explicit constexpr nullopt_t (int) {}
> +};
> +
> struct in_place_t
> {
> explicit in_place_t () = default;
> };
>
> constexpr gdb::in_place_t in_place {};
> +constexpr nullopt_t nullopt {42};
>
> /* This class attempts to be a compatible subset of std::optional,
> which is slated to be available in C++17. This class optionally
> @@ -55,6 +61,9 @@ class optional
> constexpr optional ()
> : m_dummy ()
> {}
> + constexpr optional (nullopt_t)
> + : m_dummy ()
> + {}
>
> template<typename... Args>
> constexpr optional (in_place_t, Args &&... args)
> @@ -93,6 +102,13 @@ class optional
>
> /* Assignment operators. */
>
> + optional &
> + operator= (nullopt_t)
> + {
> + reset ();
> + return *this;
> + }
> +
> optional &
> operator= (const optional &other)
> {
> --
> 2.26.2.761.g0e0b3e54be-goog
>
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